Blender 3D: Show and Work simultaneously on two or more scenes, same file
Just for the sake of completeness here I'll leave a more proper answer.

Go to File > User Preferences > Interface > Display and uncheck the option Global Scene.



The "Global Scene" option enforces displayed data from all editors to belong to the same active scene. If you disable it you can show data from different scenes in different editors if they belong to different OS Window. You will need to create an Info editor for each separate window to control which scene is displayed there.